Black Body Radiation Help

Hello! I am hoping someone could help.
I have no idea where to start on this, and have been flipping pages for an hour or so trying to figure it out.
Find the spectral range Δλ over which a blackbody's intensity B(1/2) is brighter than half of its peak value B(peak). (In other words, find the difference between the wavelengths where B(1/2) = B(peak)/2)

I have played with the Planck distribution for so long. Am I beating a dead horse? I can't seem to find out what to do with T in the plank distribution, weins law, stefan-bol..... Some guidance please!
Thanks!